Visa requirements depends on the country of origin of the newcomer.

Citizens of the following countries are not required to be in possession of a visa when entering Poland for less than 90 days:

Andorra, Argentina, Australia, Austria, Belgium, Bolivia, Brazil, Brunei, Bulgaria, Canada, Chile, Costa Rica, Croatia, Cyprus, Czech Republic, Denmark, El Salvador, Estonia, Finland, France, Germany, Greece, Guatemala, Honduras, Hong Kong (Special Administrative Region), Hungary, Iceland, Ireland, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Macao (Special Administrative Region), Malaysia, Malta, Mexico, Monaco, Netherlands, New Zealand, Nicaragua, Norway, Panama, Paraguay, Portugal, Romania, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, United Kingdom, United States of America, Uruguay, Vatican (Holy See), Venezuela

Citizens of all other countries must obtain a visa in order to enter and stay in Poland legally.

Visa approval to access Poland gives right of stay on the territory of the Republic of Poland only. To travel to the other EU state member, a new visa for the specific country is required.

To apply for a visa a passport valid for at least 6 months beyond date of arrival is required. Applications should be directed to Consulate (or Consular section at Embassy)

For the detailed information about obtaining a Polish visa visit: http://www.msz.gov.pl/Visa,requirements,2346.html

Visa types and costs

There are the following visa types in Poland for citizens of non-EU and European Economic Area countries:

• Tourist and Business: $45 (single-entry), $90 (multiple-entry)
• Transit: $20 (single-entry), $60 (multiple-entry)
• Work: $85

Certain nationals will have to pay more for visas. Reduced prices are available for students aged under 26 with appropriate identification and for children. Contact Consulate (or Consular section at Embassy) for further details.

Tourist and Business visas are valid up to 3 months from date of entry. Extensions can be arranged in Poland through the district passport office. Multiple-entry business visas are valid for 6 months. Transit visas are valid for up to 48 hours and are not required by passengers continuing their journey to a third country on the same day without leaving the transit area.

Source:
http://pl.wikipedia.org/wiki/Wiza
http://www.migrant.info.pl/en/

The work permit for foreign nationals

'New members' of the EU (Czech Republic, Estonia, Hungary, Latvia, Lithuania, Slovakia and Slovenia) and citizens of the UK, Sweden, Ireland, Malta and Cyprus are welcome to live and work in Poland without a visa or work permit.

For certain EU member states, that still have limitations in employing Polish citizens (i.e. transition periods), Poland has introduced analogous limitations. As a consequence, citizens of such countries as Germany, Austria, Spain, Greece or France must to obtain a work permit in order to work in Poland. This rule is milder in the case of citizens of Denmark, Holland, Norway and Italy (as they have less restrictive limitations).

Citizens of countries not mentioned above must obtain a work visa or permit to work in Poland.

A foreigner intending to work in Poland has to first find an employer in Poland who will agree to apply for a work permit to a voivoidship in the district where the company or institution he runs is located. A foreigner can obtain such an agreement if there are no counter-candidates among Polish citizens for the position he or she is applying for.

Sources:
http://www.polska.gov.pl/Permissions,1618.html
http://www.paiz.gov.pl/